1. Field of the Invention
The present invention relates to a continuously variable valve lift device, and more particularly, to a continuously variable valve lift device capable of reducing frictional force and improving its performance.
2. Description of Related Art
A four-stroke gasoline engine performs four strokes consisting of an intake stroke, compression stroke, power stroke and exhaust stroke. It also controls fuel flow in the cylinders and maintains an airtight space in the cylinders during the cycles.
As intake and exhaust valves are closed during the compression and power strokes, an airtight space is maintained within the cylinders. As the intake and exhaust valves are opened during the intake and exhaust strokes, fuel is introduced and combustion gas is exhausted.
Opening and closing of the intake and exhaust valves are performed by pushing ends of the valves with cams provided on a cam shaft, in which the driving force of a crank is transmitted to the cam shaft via a timing chain or timing belt.
A major factor determining the amount of intake or exhaust gas and the airtight space in the valve is a valve lift which can select acceleration or deceleration of a vehicle.
Recently, a continuously variable valve lift system has been developed and employed to vary opening period and time of intake and exhaust valves and valve lift of the intake and exhaust valves in order to improve thermal efficiency and output.
That is, the continuously variable valve lift system can optimize the opening time of the intake and exhaust valves and movement of the intake and exhaust valves such as valve lift in accordance with operational conditions of the engine.
Therefore, it can maximize the flow rate of the intake of air at acceleration or high speeds requiring high output, and minimize the effect of EGR (Exhaust Gas Recirculation) at deceleration or low speed to improve the fuel efficiency and reduce exhaust.
FIG. 1 shows a conventional continuously variable valve lift device.
The continuously variable valve lift device includes, as shown in FIG. 1, an eccentric cam shaft 10 coupled with an eccentric cam pushing a valve 1, an eccentric cam wheel 20 moved up and down by rotation of the eccentric cam shaft 10, a rocker arm 30 with a center portion rotatably coupled to an end of the eccentric cam wheel 20, a swivel link 40 coupled to one end of the rocker arm 30, a swivel cam 50 pushing the valve to open and close the valve, and a control link 60 connecting the other end of the rocker arm 30 with a control arm 61.
The operation of the conventional continuously variable valve lift system will now be described.
First of all, if the eccentric cam shaft 10 is rotated by the crank, the eccentric cam is rotated along the inner circumference of the eccentric cam wheel 20 by the eccentric cam shaft 10, and the eccentric cam wheel 20 is swiveled in a vertical direction along a certain track. The rocker arm 30 is swiveled in a vertical direction by the eccentric cam wheel 20 to swivel the control link 60 and the swivel link 40.
In this instance, when the swivel link 40 is lowered, the swivel cam 50 is rotated by the swivel link 40 to push the valve 1, so that the valve is opened or closed.
However, since the eccentric cam comes in contact with the inner circumference of the eccentric cam wheel 20 when the eccentric cam shaft 10 is rotated, the frictional force is significantly increased. There is a problem of wearing and noise occurring due to the frictional force.
Also, since the radio of gyration of the control arm 50 is separated from the eccentric cam shaft 10, it is different from the advance direction of the eccentric cam. Therefore, it is difficult to adjust the advance.
In addition, since the conventional continuously variable valve lift device has a complicated structure, much manufacturing expenses and times are needed, and thus its cost is increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.